Various types of conventional integrated circuit (IC) sockets for attaching IC packages are known. Each of the IC packages has a large number of contacts that are arranged in a matrix-like array. The IC packages are classified as pin grid array (PGA) packages, ball grid array (BGA) packages, or land grid array (LGA) packages depending on the shape of an electric contact portion of the contacts. The contacts in each of the IC packages are brought into contact with corresponding contacts arranged in a housing of the socket to establish electrical connections therebetween. The mating of the contacts in the IC package with the corresponding contacts in the socket typically causes a large contact pressure to be exerted on the socket. In cases where a large contact pressure is exerted on the socket, various methods are known to provide the socket with sufficient strength to prevent deformation of the socket. Different methods are used to prevent deformation of the socket depending on the direction of the force that is exerted on the socket.
For example, FIGS. 1 and 2 of Japanese Unexamined Patent Publication No. 2000-173735 teach a PGA socket with an insulative housing having peripheral edges reinforced by over-molding a thin metallic frame member with an insulating resin from which the housing was formed. A slide cover with a PGA package thereon is moved in a horizontal direction by a cam or a lever so that electrical connections between the socket and the PGA package are formed. Because the housing is not subjected to a large vertical force, the underside of the housing is not reinforced. Although this socket is suitable for use with PGA packages, this socket lacks sufficient strength for use with LGA packages wherein the LGA package is pressed from above the socket and a large vertical force is exerted on the socket in a direction substantially perpendicular to a printed circuit board.
To prevent deformation of a housing of a LGA socket when a large force is exerted in a vertical direction, a pair of metal reinforcements is provided. The metal reinforcements clamp the LGA package and the socket fitted with the LGA package together from opposite sides (from both front and back surface sides) of a printed circuit board to which the socket is fitted. The metal reinforcements include a loading plate or heat sink disposed on the LGA package and a board restraint plate disposed under a mount board. A screw is passed through the loading plate or heat sink and the board restraint plate at each corner thereof and is tightened by a nut to prevent deformation of the socket. The printed circuit board has apertures on a periphery thereof for accommodating the screws. This configuration, however, requires a larger footprint on the printed circuit board than that actually occupied by the socket itself. Thus, the socket size is large, a large number of parts, such as, screws, are required, and assembly is complicated. In another embodiment, the LGA package and the socket are disposed between a heat sink and a printed circuit board, and the socket is directly screwed to the printed circuit board. In this configuration, however, the printed circuit board is susceptible to warping.
Additionally, as taught in FIGS. 1 and 3 of Japanese Unexamined Utility Model Publication No. 2-86090, a lever may be used to connect and maintain electrical connections between contacts of an IC package and corresponding contacts of a socket. The lever may be adapted to be engaged with a protrusion or elastic interlocking element integrally formed with a resin housing of the socket. The lever may be locked by the protrusion or elastic interlocking element to hold the electrical connections between the contacts. Since the protrusion or the elastic interlocking element is made of resin, the protrusion or the elastic interlocking element is apt to wear-out due to friction with the lever during operation of the lever. The socket, therefore, is not durable. Forming the protrusion or the interlocking element as a separate metal member, however, increases the number of parts and the manufacturing costs.
Further, if the housing of the socket deforms when the LGA package is pressed by a cover member to form electrical connections between the contacts, the electrical contact array may become warped and deteriorate the electrical connections between the contacts. A force applied to the lever for actuation will also not efficiently be transferred, because the force will be absorbed by the deformation of the housing.